Organ chorus and celeste system utilizing randomly varying phase shift means



June 13, 1967 A. c. YOUNG 3,325,581

ORGAN CHORUS AND CELESTE SYSTEM UTILIZING RANDOMLY VARYING PHASE SHIFT MEANS Filed July 20, 1964 2 Sheets-Sheet 1 I J7 a I u a 5 :26 24; E Mix/Na CHORUS .28 R FORMATS 32 T PERCUSSION REVERBERATION 30 g 36 3 3 ETC J CELESTE 3%ceuzsrs Ego 20a g CHORUS Q ZELEsTE 2241 T- Id 72 CELESTE LIGHTS "fi 60 270 22g ww June 13, 1967 c. YOUNG ORGAN CHORUS AND CELESTE SYSTEM UTILIZING RANDOMLY VARYING PHASE SHIFT MEANS 2 Sheets-Sheet 2 Filed July 20, 1964 United States Patent ware Filed July 20, 1964, Ser. No. 383,727 6 Claims. (Cl. 841.24)

This invention relates to electrical musical instruments, generally of the organ type, and more particularly to the provision therein of improved chorus and celeste effects.

It is an object of the invention, therefore, to provide improved chorus and celeste or similar effects for electrical musical instruments.

Yet another object is to provide electrical circuitry and associated mechanisms for producing novel chorus and celeste effects which are more closely similar to these effects as produced by a pipe organ than any similar arrangements that I know of.

In pipe organ practice, a chorus effect is produced because the pipes are never perfectly in tune. Even if they are perfectly tuned, they will not stay in tune because slight changes in temperature, humidity, barometric pressure, blowing pressure, and the like, will affect some pipes more than others.

The chorus effect is most strongly heard when two or more pipes of the same general tone quality and the same pitch or octavely related pitches are sounded together. In general, therefore, there is no chorus when a single pipe is sounded, and the more pipes sounded together the greater the chorus effect, and when some stops are sounded together the effect is greater than when certain others are sounded.

The chorus effect may .be characterized as an enhancement of the music produced by sounding some pipes at their proper pitch together with the simultaneous sounding of other pipes which are slightly off pitch, with the degree of lack of perfect tuning being essentially random. As will be seen presently, in practicing the present invention the chorus effect is produced by transducing electrical signals into sound at the correct pitch and simultaneously transducing a sound signal which is slightly off pitch and which varies in frequency on a random basis relative to the central frequency, or at least in a manner which is so nearly random as to be essentially indistinguishable therefrom by the ear. Throughout this specification the word random is used in this sense; that is, the effect produced is essentially random over a long enough period of time so that repetition of the cycle usually does not occur until after the note being played has been released, or, if it is still held, the time interval will be so great that it cannot be noticed that the effect is not truly random.

The term celeste as used in organ practice is somewhat different from chorus, and covers the situation where sets of pipes are purposely tuned slightly flat and slightly sharp and sounded together so that the true frequency of the note lies between the frequencies of the two sets of pipes. In carrying out the present invention, celeste is produced in this manner; that is, there is a random variation in the frequency which is supplied to the output of the organ in such manner that both slightly sharp and slightly flat notes are sounded together, with the degree of separation between the two being variable on a random basis.

According to the circuitry of the present invention, when the celeste stop is used the effect is therefore produced even though a single key is played, so as to simulate the pipe organ arrangement in which two pipes are ice blown together to obtain the celeste effect. On the other hand, when the chorus effect is used, the amount of the chorus increases as more keys are played or as more of certain stops are used, and the effect is additive up to the point where the maximum desired chorus is obtained.

In the drawings, wherein similar characters of reference refer to similar elements throughout the several views;

FIG. 1 is a diagrammatic representation showing the general arrangement;

FIG. 2 is a diagram illustrating the circuits for the celeste and chorus portions of the instlument as applied to the swell section of an organ;

FIG. 3 is a diagrammatic representation of a photoelectric portion of the apparatus which produces the random effect previously mentioned;

FIG. 4 shows the layout of openings in a scanning disk used in the photoelectric portion of the apparatus; and

FIG. 5 is a diagrammatic representation of the control system for producing the chorus and celeste effects.

The chorus and celeste effects produced by the present invention can be applied to any section of an organ, and the application to the various sections may be the same, or minor changes which will suggest themselves may be made as between sections at the will of the designer. A typical arrangement, therefore, is illustrated in the drawings, and it may be considered, in the interest of being specific, that the system is intended for use with the organ swell section.

Referring to FIG. 1 of the drawings, the generating system 10 is shown at the left edge and will consist of the number of generators required to produce all of the notes which are to be present in the organ swell section. Various arrangements are in common use for providing such generators, and so far as the present invention is concerned it makes no difference what type generating system is used. The output from. the generators '10 is passed through the keying section 12 and, depending upon the keys being played, the outputs from certain of the generators are connected together and passed through formant circuits and circuits for supplying reverberation or percussion or other effects at 14 to the lead 16. The various control circuits in the box at 14 can, of course, be separated and connected into the general circuit at other points, if desire-d, and it may be convenient or desirable in some instances to have some of the circuitssuch as reverberation arrangements, for instance-beyond the chorus and celeste circuitry rather than ahead, in the position shown. I

The lead 16 is connected through a switch fixed contact 17 and blade 13 to an amplifier 20, the output of which feeds a speaker 22. Ordinarily, the swell control for the organ will form a portion of the output amplifier system at 20 and it needs no description since it may be considered as conventional.

The lead 16 is also connected to the chorus circuit 24 by a switch 26, and to the celeste circuit 28 by a switch 30. The output lead 32 from the chorus circuit 24 is connected to a second power amplifier 34 which may have a swell control ganged to operate with the swell incorporated in the circuit at 20, so that the two work together from a single swell pedal. From the amplifier 34 the signal passes to a second speaker 35. The lead 32 is also connected to one of two outputs from the celeste circuit, a second output 36 from the celeste circuit being connected to a contact 38, also associated with switch blade 18, such that when the blade 18 is in one position the speaker 22 is connected to the lead 16, whereas when the blade (18 is in its alternative position the speaker 22 is fed from the output lead 36 of the celeste circuit. The switch blade 18 may be ganged as indicated by the dotted line 40, so that it is shifted to contact 38 when the celeste switch is closed.

FIG. 2 illustrates the celeste and chorus circuits, the upper portion being devoted to the celeste. The input lead 31 is connected through a capacitor 44 to the grid of a triode 46, the grid also being connected through a resistor 48 and resistor 50 in series to ground. The junction between resistors 50 and 48 is also connected through resistor 52 to the cathode of tube 46. The anode of the tube is connected through a load resistor 54 to the 13+ lead 56 maintained at a potential of approximately +250 v. The anode is also connected by a lead 58 through a capacitor 60 to a lead 62 which is connected, in turn, to the cathode by way of resistor 64. A light dependent resistor 66 is also connected in parallel with the resistor 64 such that the total resistance in the circuit between the cathode and the lower terminal of the capacitor 60 depends upon the amount of light falling upon the resistor 66.

The anode is also connected through capacitor 68 to the cathode by way of a second pair of resistors 70 and 72 in parallel, the resistor 72 also being of the light dependent type.

The common junction between the resistors 70 and 72 and the capacitor 68 is also connected through a capacitor 74 to the grid of a second triode 76. This grid is also connected through resistors 78 and 80 in series to ground, and the common point between these resistors is connected through resistor 82 to the cathode which is also connected through resistors 84, 86 in parallel and thence through a capacitor 88 to the anode. Resistor 86 is also of the light dependent type and may be identical with the resistor 66. The anode is also connected through a load resistor 90 to the 13+ line 56.

The output, which is taken between the capacitor 88 and the resistor 86, is connected through a capacitor 89 to the previously referred to output lead 36.

The previously mentioned lead 62 is connected through a capacitor 92 to the grid of a third triode 94, this grid being connected through resistors 96 and 98 in series to ground, the common point between these resistors being connected to the cathode through resistor 100. The anode is connected through load resistor 102 to the 13+ line 56 and also through capacitor 104 and thence to the cathode by way of the parallel connection of resistors 106 and 108. Resistor 108, like resistors 86, 72, and 66, is of the light dependent type. The junction between resistor 108 and capacitor 104 forms the second output and is connected through resistor 110 and capacitor 112 in series to the previously mentioned lead 32 from the celeste section.

It will be recognized that the above circuit delivers the signal in opposite directions of phase shift to the leads 36 and 32, and that the amount of light falling upon the light dependent resistors will have the effect of shifting the phase of the two signals, and that the phase shift produced by change in intensity in the light falling upon the resistor 66 is additive to the effect produced by the same change in light intensity falling on the resistor 108. Similarly, the phase shift produced by the change in light intensity falling upon the resistors 72 and 86 is additive.

As will be explained presently, the light dependent resistors are so arranged with respect to their light sources that they are subjected, during operation of the celeste circuit, to a continuous change in light intensity, and there is therefore a continuous change in their resistance value which has the effect of shifting the output frequency upwardly for awhile so as to increase the pitch, and downwandly for awhile to decrease the pitch. Since'the output leads are changing phases in opposite directions, the frequency will be increased in one of the output leads simultaneously with the decrease in frequency in the other lead, since as will be seen, the light intensity changes in the opposite direction in the two channels. When the switch blade 18 of FIG. 1, therefore, is closed against contact 38 and the input switch 30 to the celeste system is closed, the effect will be to produce a signal of increased pitch at the speaker 22, for instance, simultaneously with a signal of decreased pitch on the speaker 35. After a brief interval the effect will be reversed such that the overall effect based upon the acoustic mixing of the two signals will be to cause the keyed signals (whatever they may be) to pass through cycles in which, for brief intervals, the speakers produce sound of higher and lower frequencies than the true frequency, and then substantially instantaneously pass through a condition where the signals to the two speakers are of accurate pitch, and then subsequently to pass through a cycle where again one of the speakers produces sound which is slightly sharp, while the other emits sound which is slightly fiat, the signals to the two speakers, however, having been reversed. This is accomplished on a substantially random basis so as to minimize the recognizable pattern which is characteristic of this change.

The chorus system, which comprises the bottom half of FIG. 2, has the input lead 27 connected through capacitors and 122 in series to the grid of the triode 124. The common point bet-ween capacitors 120 and 122 is connnected to ground through resistor 126. The cathode is connected to ground through resistors 128 and 130 in series, and the common point between these resistors is connected through resistor 122 to the grid. The anode is connected through load resistor 134 to the B+ line 136 maintained at a potential of approximately 250 v. (to indicate volts), and the anode is also connected through a capacitor 138 and resistors 140 and 142 in parallel to the cathode. Resistor 142 is of the light dependent type, and therefore shifts the phase of the output 124 by an amount which depends upon the light falling thereon. The output of this stagethat is, the common point be tween the capacitor 138 and the resistor 142-is connected through a resistor 144 and capacitor 146 in series to a line 1148, and this line is connected in turn through capacitors 150 and 152 in series to the previously mentioned output lead 32 which, as is shown in FIG. 1, is common with the output lead 32 of the celeste circuit.

The input lead 27 is also connected through a capacitor 154 and resistor 156 in series to a lead 158 which is connected in turn through a capacitor 160 to the grid of a second triode 162. The grid of this triode is also connected to ground through resistors 164 and 166 in series, with the common point between these resistors being connected to the cathode through resistor 168. The anode is connected to the 13+ lead 136 through resistor 170 and also by way of capacitor 172 and resistor 174 and 176 in parallel to the cathode. The common point between the capacitor 172 and resistor 176 is connected to the output lead 148 by way of resistor 178.

Input lead 27 is also connected through a resistor 180 to a lead 182 connected in turn through a capacitor 184 to the grid of a third triode 186. The lead 182 is also connected through a capacitor 188 to ground, and the unction between capacitor 154 and resistor 156 is connected to ground through a resistor 190. Also, the lead 158 is connected to ground through a capacitor 192.

The circuit of the third triode 186 is much like those previously described, and it includes resistors 194 and 196 connected in series between the grid and ground, with the common point between the resistors being connected to the cathode through resistor 198. The B+ lead 136 is connected to the anode through resistor 200, and the anode is also connected through resistors 202 and 204 in parallel, and thence through capacitor 206 in series to the cathode. The output at the junction between resistor 204 and capacitor 206 is connected through resistor 208 to the junction between capacitors 150 and 152. Resistors 176 and 204 are of the light dependent type, and may be considered as identical with resistor 142 and the light dependent resistors in the celeste portion of the circuit.

Analysis of this circuit will show that each of the three triode stages in parallel act to shift the phase, although the amount of phase shift is not as great as is accomplished by the celeste circuit, since two phase shift circuits are used in an additive capacity in the celeste system, whereas only one stage is used in the chorus system.

The three parallel phase shifting stages in the chorus system differ from each other principally in the frequency discriminating input network. This input network supplies a high frequency band of the signal spectrum to the first stage 124, a low frequency band of the signal spectrum to the lead 182, and thence to the third stage at 186, and an overlapping mid frequency band to the lead 158, and thence to the second stage at 162. This arrangement makes it possible, as will be explained presently, not only to shift the phase and thus the frequency of the output signal on a random basis, but also to achieve a random shift of the high frequencies, the low frequencies, and mid frequencies relative to each other.

Referring to FIG. 3, a photoelectric scanningrdisk 220 is shown as interposed between two celeste lamp bulbs 222 and 224 and the four light dependent celeste resistors 66, 72, 86, and 108. The scanning disk 220 is shown in greater detail in FIG. 4 and will be discussed presently. The light bulbs 222 and 224 are connected in parallel to an energizing lead 226, and this lead is connected through a switch 228 to a 7 volt terminal 230, as may be seen in FIG. 5. Closure of the switch 228 therefore energizes the lights 222 and 224 to full brilliancy such that the amount of illumination received by the resistors 66, 72, 86, and 108 depends upon the transparency of the intervening scanning disk 220. Shields, indicated at 228, are placed around the photoresistors so as to insure that the light reaching the photoresistors passes through only the desirable portions of the scanning disk 220.

An electric motor 232 drives the scanning disk 220 through a speed reduction system 234 so that the disk 220 is rotated slowly continuously. In the specific example here presented, the disk rotates at a speed of about 12 rpm.

Referring to the disk illustrated in FIG. 4, the black tracings indicate openings in the disk which are transparent to the lights 222 .and 224. The two outer rows pass light to the photoresistors such that resistors 86 and 72 are illuminated through the outer row 236, whereas resistors 108 and 66 are illuminated through the sec- 0nd row 2 38. Note that resistors 86 and 108 are at the top of the disk, whereas resistors 72 and 66 are diametrically opposite at the bottom. Also, the track 236 is symmetrical from side to side so that whenever a change in the light intensity occurs at resistor 86, the same change willtake place with respect to the resistor 72. Similarly, also, the second band 238 is of complementary pattern to the band 236, and it is slightly staggered in a clockwise direction for mechanical convenience to accommodate the resistors in such relationship that as the light increases on resistor 86, it decreases on resistor 108 and so on. It can be seen, therefore, that the outputs represented bythe leads 36 and 32 are of the same avearge phase with respect to each other, but the amount and direction of phase shift in each of the leads depends upon the additive effect produced upon the two resistors used in each of the two phase shifting circuits as effected by the light traversing both tracks 236 and 238.

Chorus light bulb 240 is energized by way of lead 242, and the light from this bulb passes through the three inner tracks 244, 246, and 248. These tracks are random with respect to each other, and the various openings in each track are random with respect to other openings in the same track. The innermost track 248, which has the fewest number of openings, controls the light falling upon photoresistor 204 which shifts the phase of the low frequency signal spectrum. The next track 246 controls the light falling upon resistor 176 and this track hasmore openings than the innermost track. Frequency shifts n the mid channel therefore occur somewhat more rapidly than they do in the low frequency channel. Similarly, also, track 244, which controls the illumination falling upon resistor 142, has still more openings, so that the rate of change in the frequency of the basic signal is more rapid for the high frequency channel. This is desirable in that it is generally typical of what occurs in the pipe organ chorus.

Although the chorus light 240 and the chorus resistors 202, 176, and 144 may be placed anywhere around the disk wherever it is convenient, this organization has been indicated at 250 in the drawing of FIG. 4.

FIG. 5 illustrates the control system for the chorus light 240 and also the circuit for the celeste lights 222 and 224, which has already been described. To the left of FIG. 5 there is shown a group of switches numbered. 252, 254, 256, 258, and 260. These switches are representative of a portion of the playing keys of the organ, and they may either be directly actuated by the playing keys, or they may be relay contacts which are actuated whenever a playing key is depressed; that is, whenever a playing key is depressed, at least within the range where it is desired to provide the chorus eifect, the playing of one key will close one switch and the playing of more keys will close successively more switches, so that the number of switches closed is equivalent to the number of keys played.

All of the contacts on one side of the switches are connected together and to the lead 240 previously mentioned. The other sides of the switches are connected to the 7- volt terminal 230, each through its own resistor 262, 264, 266, 268, and 270 respectively. Since the light bulbs used will be fully illuminated at a potential of approximately 7 volts, they will be illuminated to less intensity depending upon the number of the parallel resistance connections between the source and the bulb, which in turn depends upon the number of keys played.

In the present instance, each of the resistors 262 to 270 has a value of approximately ohms, and since the amount of the chorus effect depends upon the amount of the light falling upon the photoresistors 204, 176, and 142, there will be no chorus eifect if only one key is played, if only one stop is used, since the amount of current passing through a 100-ohm resistor is not sufiicient to produce any sensible illumination from the bulb 240. If two keys are played together such that there are two current paths in parallel, the bulb is illuminated sufiiciently to produce a very mild chorus, and the more keys that are played the greater is the chorus effect. Although it is largely a matter of choice, I have found that the maxi mum chorus should occur when about five keys are played.

At the right hand side of the drawing there is a group of switches indicated by the numerals 272, 274, 276, 278, 280, 282, and 284. These switches are contained individually in various of the stop controls so that, asvarious tabs are actuated to bring the resources of various ranks into action, one of the switches from 272 to 284 is actuated.

Switch 272 is connected on one side by a 47-ohm resistor 286 to the 7-volt terminal 230, and the other side of this switch is connected in series through the second switch 274 to a lead 288 which is a branch of the previously mentioned lead 242 which energizes the chorus light. Thus when switch 272 only is closed, nothing happens so far as the chorus light is concerned, and the same is true if switch 273 only is closed. However, whenever switches 272 and 274 are both closed, the chorus light will receive current through the 47-ohm resistor 286, and this current will be added to whatever current is received through the 100-ohm resistors 262 to 270.

Switches 272 and 274 are actuated by stop tabs which control stops having generally similar characters, so that as was mentioned near the beginning of the specification, a stronger chorus effect will be produced under conditions where two similar stops are being used at the same time.

Similarly, switches 278 and 280 are in series, with one side of the series arrangement being connected to the 7- volt source through a 47-ohm resistor 290, while the other side of this switch combination is connected to the lead 288. This switching arrangement is a duplicate of the one just described, but, as will be understood, the switches 278 and 280 are associated with a different set of stop controls which, although similar to each other, differ considerably with respect to those just described above. Thus, operation of the stop tabs which close switches 272 and 278 will not produce a chorus, but the closure of switches 278 and 280 will.

Normally, whenever the crescendo control of the organ is actuated so as to bring a number of stops into operation, a greater chorus will be desired. This can be accomplished by providing the switch 276 and 47-ohm resistor 292 connected between the 7-volt terminal 230 and the lead 288. This switch is actuated by the crescendo control, and has the same effect, so far as the chorus is concerned, as though, for instance, controls 272 and 274 were both actuated simultaneously.

In the event that it is desired to provide any of the single stops with a small amount of chorus, this can be accomplished by providing the switches 282 and 284 with associated resistors 294 and 296. These connections are essentially the same as the crescendo except that the values of the resistors 294 and 296 will ordinarily be much higher than the value of the crescendo resistor. They might, for instance, have a value of 100 ohms so that they act in the same manner as the keying resistors at the left hand side of the drawing. Although specific values have been given for the various resistors in the chorus control network, it will be appreciated that different voicers will have different opinions as to how much chorus should be present under any particular set of circumstances, and the values of the resistors can be adjusted accordingly to accomplish this. Similarly also, the stop tab switches may be wired in various way to accomplish various effects so far as the strength of the chorus is concerned.

Values of the various circuit components in the specific embodiment illustrated are as follows. Each of the triodes may be considered as being one half of a type l2AU7, and the lamps for the choru and celeste used in this particular circuit are Type #12. Several different light dependent resistors have been used successfully, and no preference is expressed as to these, it being understood that for this purpose their characteristics are similar, but minor differences may make advisable minor circuit modifications to accommodate different types.

Capacitors are as follows and are in uf unless otherwise indicated:

It will be understood that although the system has been shown and described as applied to the swell section of an organ, it may also be applied to the great and/or antiphonal and/or pedal sections for instance. In some instances it may be desired to supply additional tracks on the scanning disc and associated lights and photoresistors for additional sections. Also, of course, the same tracks can be used by arranging lights and associated photoresistors at other places along any one of the existing tracks where they do not interfere with those already present, for instance. Various combinations of these arrangements can, of course, also be used. Similarly, also, it may in some instances be sufficient simply to connect the outputs of two or more sections together and use the circuits as shown for two or more sections rather than simply for the swell section. In the main, the cost of the instrument may well be the determining factor as to just what variation is used.

From the above description of a preferred embodiment of my invention it will be appreciated that variations may be made without departing from the scope and spirit of the invention, and that, therefore, the scope of the invention is to be measured by the scope of the following claims.

What is claimed as new and desired to be secured by United States Letters Patent is:

1. A chorus system for a musical instrument having playing keys comprising a source of electrical sound signals, an output system, a channel connected between the source and the output system, said channel having means to shift the phase of the signal passing therethrough progressively upwardly and then progressively downwardly on a cyclical basis, control means for lengthening and shortening and for determining the amplitude of the individual cycles on a substantially random basis, said control means including means for affecting the amplitude of phase shift on the basis of the potential applied to a terminal, and means connected to the terminal to apply a potential thereto when a playing key is actuated and to progressively change the potential in a direction to produce greater amplitude of phase shift as rogressively more keys are actuated together.

2. The system called for in claim 1, in which stop controls are provided and in which means responsive to the actuation of certain of the stop controls are provided to change the potential in the direction to produce greater phase shift when certain combinations only of the stop controls are actuated together.

3. A chorus system comprising a source of electrical sound signals, a first and a second output system, a channel connecting the source to the first output system, a second channel connecting the source to the second output system, said second channel having means to shift the phase of the signal passing therethrough progressively upwardly and then progressively downwardly on a cyclical basis, control means for lengthening and shortening and for determining the amplitude of the individual cycles on a substantially random basis, said phase shifting means including light dependent resistors with the degree of phase shift depending upon the light falling upon said resistors, the control means including light sources illuminating said light dependent resistors and an intervening moving variable masking means to determine the amount of light from said sources reaching said resistors depending upon the position of the masking means, and means for applying a potential to the light source when a playing key is actuated and to increase the potential to the light source progressively as additional keys are actuated together.

4. A chorus system comprising a source of electrical sound signals, a first and a second output system, a channel connecting the source to the first output system,.a second channel connecting the source to the second output system, said second channel having means to shift the hase of the signal passing therethrough progressively upwardly and then progressively downwardly an a cyclical basis, control means for lengthening and shortening and for determining the amplitude of the individual cycles on a substantially random basis, said phase shifting means including light dependent resistors with the degree of phase shift depending upon the light falling upon said resistors, the control means including light sources illuminating said light dependent resistors and an intervening moving variable masking means to determine the amount of light from said sources reaching said resistors depending upon the position of the masking means, and means actuated by certain of the stop controls for applying a potential to the light source when certain combinations only of the stop controls are actuated.

5. A chorus system comprising a source of electrical sound signals, a first and a second output system, a channel connecting the source to the first output system, a second channel connecting the source to the second output system, said second channel having means to shift the phase of the signal passing therethrough progressively upwardly and then progressively downwardly on a cyclical basis, control means for lengthening and shortening and tor determining the amplitude of the individual cycles on a substntially random basis, said phase shifting means including light dependent resistors with the degree of phase shift depending upon the light falling upon said resistors, the control means including light sources illuminating said light dependent resistors and and intervening moving variable masking means to determine the amount of light from said sources reaching said resistors depending upon the position of the masking means, and control means for applying a potential to the light source when said control means is actuated.

6. A chorus system for a musical instrument having playing keys and a group of stop controls comprising a source of electrical sound signals, an output system, a channel connected between the source and the ouput system, said channel having means to shift the phase of the signal passing therethrough progressively upwardly and then progressively downwardly on a cyclical basis, control means for lengthening and shortening and for determining the amplitude of the individual cycles on a substantially random basis, said control means including means for affecting the amplitude of phase shift on the basis of the potential applied to a terminal, and means including said group of stop controls and said playing keys connected to the terminal to apply a potential thereto when a playing key is actuated and to progressively change the potential in a direction to produce greater amplitude of phase shift as progressively more of the stop controls in said group are actuated together.

References Cited UNITED STATES PATENTS 3,004,459 10/1961 Jones 84-119 X 3,004,460 10/1961 Wayne 84-l.19 X 3,083,606 4/1963 Bonham 84-1.25 3,255,297 6/1966 Long 84-125 3,258,519 6/1966 Young 841.25

ARTHUR GAUSS, Primary Examiner.

B. P. DAVIS, Assistant Examiner. 

1. A CHORUS SYSTEM FOR A MUSICAL INSTRUMENT HAVING PLAYING KEYS COMPRISING A SOURCE OF ELECTRICAL SOUND SIGNALS, AN OUTPUT SYSTEM, A CHANNEL CONNECTED BETWEEN THE SOURCE AND THE OUTPUT SYSTEM, SAID CHANNEL HAVING MEANS TO SHIFT THE PHASE OF THE SIGNAL PASSING THERETHROUGH PROGRESSIVELY UPWARDLY AND THEN PROGRESSIVELY DOWNWARDLY ON A CYCLICAL BASIS, CONTROL MEANS FOR LENGTHENING AND SHORTENING AND FOR DETERMING THE AMPLITUDE OF THE INDIVIDUAL CYCLES ON A SUBSTANTIALLY RANDOM BASIS, SAID CONTROL MEANS INCLUDING MEANS FOR EFFECTING THE AMPLITUDE OF PHASE SHIFT ON THE BASIS OF THE POTENTIAL APPLIED TO A TERMINAL, AND MEANS CONNECTED TO THE TERMINAL TO APPLY A POTENTIAL THERETO WHEN A PLAYING KEY IS ACTUATED AND TO PROGRESSIVELY CHANGE THE POTENTIAL IN A DIRECTION TO PRODUCE GREATER AMPLITUDE OF PHASE SHIFT AS PROGRESSIVELY MORE KEYS ARE ACTUATED TOGETHER. 